Thixotropic lubricating grease containing polycarboxylic acid soap



United dtates atent @fiice 2,710,838 Patented June 14, 1955 THIXOTROPIC LUBRICA'HNG GREASE CONTAHN- ING POLYCARBUXYLKC ACE SQAP No Drawing. Application January 9, 1352, Serial No. 265,712

14 Claims. (Cl. 252-41) The present invention relates to an improved thixotropic lubricating grease, that is, a grease which has the properties of softening, or partially liquefying, upon being worked mechanically and quickly reverting to its relatively solid normal structure after working has been discontinued.

Lubricating greases are commonly used in place of lubricating oils in situations where liquid lubricating oils are not satisfactory. In some cases the bearings, housings or other operating parts to be lubricated are not, or cannot be made sufiiciently liquid tight to prevent undue loss of liquid lubricants. Also, it may be unduly expensive to provide liquid tight housings on oil lubrication systems. Greases are used in such cases because they are much less subject to leakage. Certain types of gears, especially large gears, and numerous types of antifriction bearings can be better lubricated with greases than with oils for similar reasons. The greases remain in situ Whereas the liquid lubricants would drain away and leave the parts inadequately protected.

For some types of lubrication, however, it is desirable to have a certain degree of fluidity even in the lubricating grease. If a lubricant is too firm and channels too completely, the operating parts may be starved for lubricant and unnecessary wear and damage may result. On the other hand it may not be possible to employ a completely liquid substance and compromises are often necessary.

The present invention is based on the discovery that normally solid lubricating grease can be made thioxtropic to an accurately controlled degree by incorporating therein a soap of aliphatic polycarboxylic acid of high molecular weight. These polybasic acid soaps, especially those derived from acids having a molecular weight over 200, or preferably over 250 and up to about 3000, impart thixotropic properties to greases to a remarkable degree. They are very much dilierent from the soaps of normal fatty acids in this respect.

Conventional lubricating greases are ordinarily prepared by dispersing in a suitable lubricating oil, usually of mineral base, an appropriate quanitity of metal soap of long chain fatty acids. Thus, the sodium or calcium soaps of stearic and oleic acids and their homologues are commonly used although some of the other fatty acids may be used alone or in mixture therewith. These conventional fatty acid soaps are not substantially thixotropic and in fact some of the greases where they are used tend to harden somewhat upon being worked mechanically. According to the present invention the desired properties of thixotropy may be quite rigidly controlled by adjusting the relative proportions of the conventional soaps with those of the new type high molecular weight polycarboxylic acid soaps.

Where a high degree of thixotropy is required, the entire soap thickener may consist of the high molecular Weight polycarboxylic acid soaps especially soaps of the alkali metals. The sodium soaps are preferred although although potassium and lithium soaps may be used. The lithium soap has been found to have outstanding proper- I 2; ties of water solubility. Compared with the lithium soaps of normal long chain fatty acids which are quite water insoluble, these new soaps have unusual properties.

For many applications of greases, water insolubility is highly desirable, but in enclosed gear boxes and the like to which moisture may have occasional access in small quantities, it is sometimes desirable to have a small amount of water solubility in the grease. In such instances small amounts of water may actually be absorbed by the grease, preventing them from being repelled from the grease and onto the metal surfaces, causing rust and corrosion. Hence, the lithium soaps of these high molecular weight polybasic acids have a peculiar utility for special purposes, in addition to their strong thixotropic property.

In general, the compositions of the present invention comprise about to by weight of lubricating oil, preferably of mineral base, although the synthetic oils may be used if desired. The synthetic oils of difunctional structure, e. g. polyglycols, polyglycol ethers, dibasic acid esters, complex esters of glycols and dibasic acids, etc., are excellent oil constituents, provided the soaps are formed or added in such a manner as to avoid decomposition of the oil. The thickening agent preferably consists of about 5 to 25% by weight of soap, of which at least 25% is of the high molecular weight polybasic, preferably essentially dibasic acid type. Suitable acids have a molecular weight of at least 200 or 250 and an average of at least 1.75 carboxyl groups per molecule. Preferred molecular weight ranges are between about 500 and 2500. Along with these polybasic acid soaps may be used the ordinary long chain fatty acid soaps, provided they do not constitute more than about 75% of the total soap content. It is preferred that at least half of the total soap be of the polybasic acid type. For some purposes all or nearly all the soap may be of the latter type.

A specific preferred composition comprises about 88 to 90% by Weight of mineral base lubricating oil and about 10 to 12% of alkali metal soap, one-half or more of which is a soap of substantially dibasic and substantially saturated aliphatic acid of molecular weight in the neighborhood of 1000. A particularly suitable acid is a product sold by Rohm and Haas under the trade name VR1. This product has an average molecular weight of about 1000 and an average of just slightly less than two carboxylic acid groups per molecule. It has a typical acid number of about 150, an iodine number of 36, a saponification number of about 172, and a low content, about 3.7%, of unsaponifiable matter. Its moisture content is low, typically about 0.86%.

It will be understood of course that conventional antioxidants such as one of the phenyl naphthyl amines may be used and that other additives such as tackiness agents,

" metal deactivators, thickeners and the like may also be employed. The invention will be more particularly understood by reference to the following specific examples.

EXAMPLEI Percent VR-l acid (Rohm and Haas, mol. wt. about 1000) 11.0 NaOI-I 1.3 Phenyl alpha naphthylamine 0.5 Mineral oil of about 45 S. S. U. viscosity at 2 0 F 87.2

Preparation The VR-l acid and about one-third of the mineral oil were mixed together and heated while stirring to about F. A 25 aqueous solution of sodium hydroxide was then added and the resulting soap concentrate was dehydrated at 225250 F. The balance of the mineral 3 oil was then added. and the mixture heated until it melted at about 380 F. The inhibitor was then added and the heat was discontinued, the product being allowed to cool. On cooling a smooth, transparent, solid grease resulted. It was homogenized to a smooth unctuous product.

Properties Penetration 77 F., mm./10:

Unworked 175. Worked 60 strokes 180. Worked 100,000 strokes 202 (after standing one hour after working). Dropping point, F 325.

On working this grease the product became semifluid but it did not completely lose its solid body. On standing without working, the grease quickly recovered its original solid structure and consistency.

The above thixotropic property can be governed or controlled by the combined soap of a mixed high molecular weight acid and a typical high molecular weight acid of conventional type such as stearic or Hydrofol Acid 51" or 54 (saturated acids of about C18 average chain length, obtained by hydrogenating fish oil acids).

EXAMPLE 11 Another composition was prepared, using the following ingredients in the weight proportions indicated:

Operation in roller bearing results in the product becoming soft, penetration 350/10. On standing Without working the product approaches its original consistency or penetration value. This product does not soften to the extent of the product in Example I, and therefore, is not as satisfactory for some types of gear or roller bearing lubrication. In other applications it may be more desirable, however, particularly where some degree of channeling is required.

Grease prepared from the lithium soap of VR-l acid retains the same thixotropic characteristics of the sodium soap. It has been found, as indicated above, that the lithium soap products are somewhat water soluble as compared with the usual Water insolubility or repellency for conventional lithium soap greases.

EXAMPLE Ill Another composition, made according to the present invention, had the following ingredients in proportions by weight:

Percent "VR-l acid 9.00 LiOH H2O 1.17 Phenyl alpha naphthylamine 0.75 Zinc naphthenate 0.75

Mineral oil of about 55 S. S. U. viscosity at Tne product was prepared in the same way as Example 1. On cooling, the soap was not completely dispersed. Passage through a Morehouse Mill (homogenizer) thoroughly dispersed the soap, however, forming an excellent grease. The product was smooth in texture and had the following properties:

Penetration, 77 F., mm./l0:

Unworked 250.

Worked 60 strokes 265.

Worked 100,000 strokes 375 immediately after working, 275 after standing 30 minutes.

Water solubility Soluble.

iv'hile the water solubility of the above grease is undesirable in some applications, this solubility may be controlled by mixing the special polybasic acids and the conventional soap making acids, such as stearic acid, etc., and forming the lithium soap of these mixed acids. A grease of this type then has only limited water adsorption properties which can be controlled. Small amounts of water entering the bearing, gear, or other mechanism are absorbed by the grease. Water insoluble greases, on the other hand, cause all moisture to be repelled and forced against the metal surfaces. Rust results, where the metal parts are of iron or steel.

EXAMPLE IV Another composition had the following ingredients (by weight:

Mineral oil of about 50 S. S. U. viscosity at Prepared similar to Example I.

Properties-limited water solubility as shown by water Washing test-25% washed out of bearing ANG-25 test, vs. 100% washed out for Example III.

What is claimed is:

1. A lubricating grease composition consisting essentially of a lubrictaing oil thickened to grease consistency with metal soap, said soap comprising a sufficient amount to substantially improve thixotropy of the grease, amount- ?"g to at least 25% by weight of said soap, of an alkali metal soap of saturated aliphatic polycarboxylic acid material having an average molecular weight in the neighborhood of 1000 and having an average of at least 1.75 and not substantially more than 2 carboxyl groups per molecule.

2. Composition according to claim 1 wherein the lubricating oil is a mineral base oil.

3. Composition according to claim 1 wherein the lubricating oil is a synthetic ester of difunctional structure.

4. Composition according to claim 1 wherein the alkali metal soap comprises at least 50% of said polycarboxylic acid soap.

5. Composition according to claim 1 wherein the alkali metal soap is sodium soap.

6. Composition according to claim 1 wherein the alkali metal soap is lithium soap.

7. A thixotropic lubricating grease composition comprising a major proportion of mineral base lubricating oil, thickened to a grease consistency with 5 to 25% by weight, based on the total composition, of a soap thickener containing at least 90 wt. of alkali metal soap of saturated aliphatic carboxylic acid material having an average of at least 1.75 and not substantially more than 2 carboxyl groups per molecule and a molecular weight in the neighborhood of 1000, said thickener containing 0 to 10% based on thickener of alkali metal soap of fatty acid of the C12 to C24 range.

8. Composition according to claim 7 wherein the alkali metal is sodium.

9. Composition according to claim 7 wherein the alkali metal is lithium.

10. A lubricating grease composition comprising about 88 to 90% by Weight of mineral base lubricating oil and 10 to 12% of alkali metal soap, at least half of said soap being of a dibasic saturated aliphatic acid of molecular weight of about 1000.

11. Composition according to claim 10 wherein the alkali metal is sodium.

12. Composition according to claim 10 wherein the alkali metal is lithium.

13. Composition according to claim 10 wherein subsubstantially all of the soap is of dibasic acid.

14. A lubricating grease composition comprising 75 to 95% by weight of a lubricating oil thickened to grease consistency with alkali metal soap, said soap consisting essentially of a sufiicie-nt amount substantially to improve thixotropy of the grease, amounting to at least 25% by weight of said soap, of an alkali metal soap of saturated aliphatic polycarboxylic acid material having an average molecular weight in the neighborhood of 1000 and having an average of 1.75 to 2 carboxyl groups per molecule.

References Cited in the file of this patent UNITED STATES PATENTS 2,487,080 Swenson Nov. 8, 1949 2,495,651 Butcosk Jan. 24, 1950 2,538,373 Knowles et al Oct. 31, 1950 2,555,104 Ashley et al. May 29, 1951 2,583,607 Sin'anni et a1. Jan. 29, 1952 2,599,553 Hotten June 10, 1952 

1. A LUBRICATING GREASE COMPOSITION CONSISTING ESSENTIALLY OF A LUBRICATING OIL THICKENED TO GREASE CONSISTENCY WITH METAL SOAP, SAID SOAP COMPRISING A SUFFICIENT AMOUNT TO SUBSTANTIALLY IMPROVE THIXOTROPY OF THE GREASE, AMOUNTING TO AT LEAST 25% BY WEIGHT OF SAID SOAP, OF AN ALKALI METAL SOAP OF SATURATED ALIPHATIC POLYCARBOXYLIC ACID MATERIAL HAVING AN AVERAGE MOLECULAR WEIGHT IN THE NEIGHBORHOOD OF 1000 AND HAVING AN AVERAGE OF AT LEAST 1.75 AND NOT SUBSTANTIALLY MORE THAN 2 CARBOXYL GROUPS PER MOLECULE. 